In general, a polyimide (hereinafter referred to as “PI”) resin denotes a high heat-resistant resin which is prepared by solution polymerizing an aromatic acid dianhydride(s) and an aromatic diamine(s) or an aromatic diisocyanate(s) to produce a polyamic acid derivative, and then by carrying out a dehydration ring-closure reaction at a high temperature, followed by imidization.
A polyimide resin is generally prepared by polymerizing an aromatic acid dianhydride(s), such as pyromellitic dianhydride (PMDA), biphenyl tetracarboxylic dianhydride (BPDA), etc. and an aromatic diamine component(s), such as oxydianiline (ODA), p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), methylene dianiline (MDA), bisaminophenyl hexafluoropropane (HFDA), etc.
A polyimide resin is ultra-highly heat-resistant, insoluble, and non-meltable with excellent properties, such as thermo-oxidative stability, excellent heat-resistance, radiation resistance, low temperature properties, or chemical-resistant properties, and thus, is finding wide applications in a variety of fields including those of advanced heat-resistant materials, such as automotive materials, aircraft materials, spacecraft materials, etc., and electronic materials such as insulation coating materials, insulating films, semiconductors, electrode protective films for TFT-LCDs, etc.
Recently, such a resin is widely used as coverlays for portable electronics and communication devices. Coverlays are known as barrier films for protecting electronic components such as printed circuit boards, leadframes of integrated circuit packages and the like. A need exists, however, for coverlays to be increasingly thin and slim, while having security, portability, visual effects and optical properties including shielding for electronic components or mount components.
For example, the Korean Patent Publication No. 10-2015-0076525 discloses an adhesive composition comprising (A) a non-halogen based epoxy resin, (B) a thermoplastic resin, (C) a curing agent and (D) an inorganic filler, a copper clad laminate and a coverlay film using the same. It describes, however, that said film has a thickness of 5 to 200 μm, which still fails to meet the slimness requirement.